This invention relates to high-voltage high-power multiphase circuit breakers, and more particularly relates to a novel operating mechanism for such circuit breakers which enables ganged closing and individual opening of each of the poles or phases of the breaker. In the event that one of the poles is "stuck closed", the individual opening feature enables the other poles to open. A stuck-closed phase can be caused by any of numerous conditions including welding of contacts of interrupters, breakage or jamming of parts of the interrupter or breaker, and the like. If for some reason, one of the breaker phases cannot open, and also prevents the other two phases from opening, the chance of escalating a single line-to-ground fault into a multiphase fault is greatly increased.
High-power high-voltage circuit breakers of the type to which the present invention applies are well known in the art, and are typically shown in U.S. Pat. Nos. 3,836,741 (PC-94), 3,879,591 (PC-170), 3,885,114 (PC-166) and 3,889,083 (PC-165), each of which are owned by the assignee of the present invention and which are incorporated herein by reference. In breakers of this type, it is common to provide a single operating mechanism which is contained in a housing secured to one of the phases. An operating rod extends from the single operating mechanism to each of the breaker phases for operating all phases from the single operating mechanism. Thus, each breaker phase is simultaneously opened and closed through the single operating mechanism and interconnected operating rod. This arrangement permits the substantial simultaneous closing of each breaker phase, which is necessary for the power transmission system stability.
High-power circuit breakers have also been designed in the past with each phase or pole having its own operating mechanism for both closing and opening the phase. Thus, each phase can be independently tripped so that, if one phase is stuck closed, the other two phases can still open, thereby decreasing the chance that a line-to-ground fault will escalate to a multiphase fault which would, in turn, cause a major system outage. These independent poles are also arranged to close at the same time, but experience has shown that, because of the added parts in the closing systems, such as closing anti-pump relays, solenoid-operated, pneumatic or hydraulic valves, and the like, plus the different travelling times of the breaker contacts of different phases from open to closed positions, there is an erratic pole spread upon closing. This pole spread is deleterious to the system stability due to overvoltages during closing of the breaker in a high-voltage high-power system.